White Bear Photonics offers NIST traceable standards for reflection and transmission measurements.  Ultraviolet and visible spectrophotometers are fundamentally both accurate and precise but it is vital to check instrument performance on a regular basis to ensure that it is operating within satisfactory parameters. The reference materials provided are based on materials which have been used by national reference laboratories such as National Institute of Standards and Technology (NIST). When used in periodic testing of your instrument’s performance you build a quality control database of the operating characteristics of your specific instrument.